The Collapse Floor: A Minimum Mass for Black Holes Formed by the Collapse of Fermionic Matter

In Einstein-Cartan gravity the spin of fermionic matter sources torsion, and eliminating torsion leaves a repulsive correction to the effective density that balances the matter term at a finite density: for neutron matter, in the incoherent spin prescription, rho_A = 9.72e54 g/cm^3. This paper converts that pinned density into a statement about objects. During the collapse of a spherical mass M, the mean density reaches rho_A at R_A(M) = (3M/4 pi rho_A)^(1/3) while the Schwarzschild radius grows linearly; the two radii cross at M_A = sqrt(3/32) hbar c/(G mu) = 8.66e13 g for neutron matter, where mu is the gravitating mass per spin carrier. Below M_A the collapse halts at the bounce density before any horizon forms, so M_A is a formation floor for black holes made by the collapse of fermionic matter, and by the same crossing the endpoint of Hawking evaporation for such objects (Hawking temperature at the floor 1.42e12 K). Carrier law rho_A(mu) = mu^2 c^4/(pi G hbar^2) with thresholds tabulated for electron, neutron, hydrogen-plasma, and carbon-oxygen carriers. The paper states its register condition at full size: the floor is exact in the nonrelativistic spin-fluid register in which rho_A is pinned; in the exact Fermi-gas register the same construction returns a threshold of order the Planck mass. Deposit contains the paper (PDF and LaTeX source) and the computation file with its output; every printed number is reproduced by re-running it.